Conventional rinse-added fabric softening compositions contain fabric softening agents which are substantially water-insoluble cationic materials usually having two long alkyl chains. Typical of such materials are di-stearyl dimethyl ammonium chloride and imidazolinium compounds substituted with two stearyl groups. These materials are normally prepared in the form of an aqueous dispersion or emulsion, and it is generally not possible to prepare such aqueous dispersions with more than about 7% of cationic material, while still retaining acceptable viscosity and stability characteristics. This, of course, limits the level of softening performance achievable without using excessive amounts of product, and also adds substantially to the distribution and packaging costs, because of the need to market such dilute solutions of the active ingredient. Another advantage of a more concentrated fabric softening composition is that it permits the consumer to exercise choice in the type of performance desired, in that the concentrated product can either be used as such or can be diluted to a conventional concentration before use. This opens up the possibility of supplying the concentrated fabric softening composition in a more economically packaged form intended for making up by the consumer into a conventional bottle.
The problem of preparing fabric softening compositions in concentrated form suitable for consumer use has already been addressed in the art, but the various solutions proposed have not been entirely satisfactory. It is generally known (for example in U.S. Pat. No. 3,681,241) that the presence of ionizable salts in such compositions do help reduce viscosity, but these materials do not offer the additional benefit of enhancing the softening performance of the compositions. The use of certain special processing techniques has also been suggested in this regard (for example in U.S. Pat. No. 3,954,634) but again this does not provide a complete and satisfactory solution, and it is not an easy matter to adopt this type of process on a commercial scale. Dutch patent application No. 6706178 relates to viscosity control in fabric softening compositions with up to 12% of cationic softener, and suggests the use of low molecular weight hydrocarbons for this purpose. Finally, German patent application No. 25 03 026 discloses a complex softener/disinfectant composition in which a long chain fatty alcohol used at a relatively low ratio of cationic softener to alcohol is suggested as a solubilization aid.
In verbruggen European patent application No. 79200801.3, concentrated fabric softener compositions are disclosed which contain small amounts of certain hydrocarbon, fatty acid, fatty acid ester and fatty alcohol materials as viscosity reducing agents. It has been found, however, that although these materials are excellent in reducing the viscosity of concentrated fabric softener compositions at temperatures below the Krafft point of the cationic softener, they are very much less effective as viscosity reducing agents in concentrated compositions at temperatures close to or above the Krafft point of the softener. This means for instance, that in the case of distearyl dimethyl ammonium chloride cationic softener (Krafft point above 37.degree. C.), compositional viscosity tends to increase markedly from about 30.degree. upwards, so that at a temperature of about 40.degree. C. compositions based thereon become virtually unpourable.
It has now been discovered that viscosity control in concentrated fabric softener compositions can be significantly improved both at normal and higher temperatures, by the use of a two-component viscosity regulator system comprising, firstly, a hydrophobic component selected from specified hydrocarbons, fatty acids, fatty acid esters and fatty alcohols, and secondly, a water-soluble cationic polymeric component of specified polymer molecular weight and chemical type.
The use of polymers in cationic fabric softener compositions is disclosed generally in European Published patent application No. 2085 which teaches the use of cationic polymers for minimizing the effect of surfactant carry-over from a machine wash cycle into the rinse. However, the patent application does not disclose the use of a combination of hydrophobic and cationic polymer materials as defined herein in concentrated fabric softener compositions, nor does it recognize the beneficial effect of this combination of materials in regulating the viscosity of concentrated fabric softener compositions.
The present invention thus provides a concentrated liquid fabric softener composition having improved viscosity characteristics at both normal and elevated temperatures and having good storage stability and other physical characteristics necessary for consumer use. The present invention also provides a cost-efficient, physically acceptable fabric softener composition providing softening benefits across the range of natural and synthetic fabric types, based on water-insoluble cationic softener as the major active component of the composition.